Welcome to the forum and smart move asking for advice before you buy. Some of the longer term members can probably be of more help, but I'll tell you what I wish I had ask, known, or done before I bought my first skies this year. First, if at all possible ride the ski. Just because is cranks on the trailer and sounds good there doesn't mean it will run well in the water. Second, check the compression of the engine, easy test with inexpensive tool. Third, look at the fuel lines. Gray lines must be replaced. If they are gray it also means the carbs will most likely need to be at least cleaned or rebuilt. The fuel selector will also need to be cleaned or replaced. Check the impeller and wear ring for any damage or signs of items such as rope being caught up in them. Same with the intake grill. All except the compression are things that can be fixed by you if you have a little mechanincal skills.
I don't know about OK, but price is a little high for SC especially this time of year. I paid $3500 for both a 2001 GTX and 1997 GTX on a double trailer in July. But would have passed if I had know the above. Compression was good on both my skies but had to change the fuel lines, rebuild carb and wear ring on one, and install a new fuel pump on the other and it's still not right. Had I taken a test ride I would have know right away to pass. So now I'm closer to $5500 on my two and still at least $500 away from getting the second one right. Just my two cents.